Conventional imaging apparatuses such as electronic still cameras and video tape recorders (VTRs) utilize an imaging system such as that shown in FIG. 1. Briefly, the system comprises an imaging optical system 1 composed of an imaging lens, a diaphragm stop, a shutter, etc.; an imaging device 2, such as a charge-storage solid-state imaging device (CCD) placed behind the imaging optical system 1; and a color filter assembly 3 provided on the light-receiving surface of the imaging device 2 which consists of a red (R), a green (G) and a blue (B) filter typically associated with pixels. The imaging device 2 performs photoelectric conversion of the optical image of the subject and then reads information by "horizontal" and "vertical" scanning to produce a video signal generated for each pixel on a real time basis. The output video signal is then amplified by a preamplifier 4 to an amplitude level which allows for signal processing.
The video signal produced on a real time basis output from the preamplifier 4 is fed into a color separator circuit 5 where it is separated into three color signals of red (R), green (G) and blue (B). The color signals are then fed into a white balance adjusting circuit 6 and the amplitude levels are adjusted in such a way that an optimal white color is obtained when an image is reproduced from the color signals. The color signals produced from the white balance adjusting circuit 6 are passed through a gamma-correcting circuit 7 which corrects for the tonal characteristics of a CRT and are thence supplied to a matrix circuit 8 where they are converted to a luminance signal Y and color difference signals R-Y and B-Y. Luminance signal Y is subsequently delivered to sync mix circuit 40 to thereby produce output signal Y+S which contains sync information. These signals Y+S, R-Y and B-Y can be recorded on a magnetic recording medium, supplied to a video reproducing monitor television or used in other applications.
The imaging apparatus described above has an automatic exposing (AE) capability by which the aperture or shutter speed is controlled in such a way that the exposure amount is automatically adjusted to ensure optical setting of the quantity of light incident upon the apparatus. The AE process comprises the steps of detecting the intensity of light received from a subject subtended by a given angle of viewing and then automatically controlling the aperture or shutter speed to enable imaging under optimal conditions for the photoelectric conversion characteristics of the imaging device.
Even if such AE capability is built into the imaging apparatus, satisfactory results are not always attained. For example, if a dark subject of interest A to be imaged is located in a brighter background scene B, such as shown in FIG. 2, the darker subject of interest A will be reproduced as an obscure image due to contrasting brightness. Similarly, if a picture is taken with an increased amount of light reception from the subject of interest A, the background scene B will become dead white. Conversely, if the subject of interest is a person in white clothes standing in a dark background, the clothing will appear extremely bright and as a result, difficult to perceive.